1 Preparation of MQ resin
MQ silicone resin is usually prepared by sol-gel method. The main raw material of M chain is hexamethyldisiloxane (MM) or trimethylchlorosilane. The raw material of Q chain is mainly water glass (silicic acid). Sodium) or tetraethyl orthosilicate (TEOS). Due to the difference in raw materials of Q chain, it is mainly divided into tetraethyl orthosilicate method and water glass method. The product prepared from ethyl orthosilicate has better performance, but the cost is higher, which limits its application range; the water glass method has cheap and easy to obtain raw materials, and has good product performance and large market value.

2 MQ silicone resin in silicone rubber
Silicone rubber has a variety of excellent properties, but its mechanical properties such as compressive strength and tear strength are poor, and it cannot meet the requirements of the process. It is necessary to add a filler to modify it. When MQ silicone resin is used as reinforcing filler, it can increase the strength of the rubber matrix without increasing the viscosity of the system too fast for subsequent operation, and the vulcanized rubber obtained has good transparency.

The organic part of MQ silicone resin can improve its compatibility with silicone rubber and enhance the viscosity. The silica oxygen chain energy-saving improves the mechanical strength, cohesive strength, peel strength and high temperature resistance of silicone rubber, and plays a reinforcing role. The addition type vulcanized silicone rubber is mainly composed of a vinyl-containing raw rubber, a reinforcing filler, a hydrogen-containing silicone oil crosslinking agent, and a platinum catalyst. Under the action of the platinum catalyst, the vinyl-containing MQ resin can chemically combine with the raw rubber by a hydrosilylation reaction with the SiH crosslinking agent, thereby forming a three-dimensional network structure to reinforce. As the amount of MQ silicone resin increases, the hardness, tensile strength, tear strength, adhesion properties, and crosslink density of silicone rubber gradually increase to an optimum value. The reason is that MQ silicone resin has relatively small molecular mass, relatively high vinyl content, good compatibility and dispersibility in silicone rubber, and chemical bonding with silicone rubber. However, when the crosslink density is too large, the cross-linking points are unevenly distributed, stress concentration is formed, the silicone rubber becomes hard and brittle, and the silicone rubber is easily broken under stress. The curing time is prolonged with the increase of the amount of MQ. This is because the MQ molecule is small and the vinyl content is high, which can preferentially react with the hydrogen-based silicone oil, thereby delaying the reaction of the silicon hydride with the vinyl rubber until the MQ is consumed. As the amount of MQ resin increases, the dielectric constant of silicone rubber increases to a maximum and approaches equilibrium. However, if the amount of MQ resin is too large, the cross-linking of the silicone rubber is excessive, which limits the activity of the polar group, so that the dielectric constant tends to be stable. However, the dielectric properties of silicone are still lower than those of ordinary rubber.

The condensed vulcanized silicone rubber is mainly composed of a silicone rubber containing a terminal hydroxyl group or an alkoxy group, a reinforcing filler, a crosslinking agent and a catalyst. After the catalyst or the action of moisture in the air, the crosslinking agent hydrolyzes to form silanol, thereby undergoing a condensation reaction with the raw silicon silyl group to form a three-dimensional network structure, which is vulcanized into an elastomer. When MQ silicone resin is mixed with silicone rubber, it has a thickening and reinforcing effect, which makes silicone rubber have excellent mechanical properties. However, when subjected to electromagnetic radiation and vacuum ultraviolet irradiation, silicone rubber will age, deform and crack, and the performance will also change. difference. The main reason for the decrease in the quality and performance of the silicone rubber caused by irradiation is the escape of unreacted low molecular substances in the vulcanizate under irradiation, the breakage of the macromolecular network structure, and the degradation or crosslinking of the molecular chain. In order to make the silicone rubber resistant to radiation, a radiation-resistant filler such as nano-TiO2 may be added thereto.

3 MQ resin in pressure sensitive adhesive
Silicone pressure sensitive adhesives are a special type of adhesive consisting of silicone (usually MQ silicone), silicone rubber, catalysts, crosslinkers and other additives. Silicone pressure sensitive adhesives mainly include solvent type, high solid content type, solventless type, emulsion type, radiation curing type, resin modified type, biodegradable type and functional type.

Since the solvent type contains a large amount of volatile organic substances, the solvent volatilization is likely to cause serious pollution to the environment upon curing. Nowadays, environmental protection is receiving more and more attention. The silicone pressure-sensitive adhesive industry is developing with environmentally-friendly and low-cost products, and researching new products such as biodegradable and radiation-curable. MQ silicone resin mainly plays a role of thickening and reinforcing. The silanol or vinyl group in MQ resin can be prepared by condensation reaction with hydroxyl group of silicone rubber or hydrogen siloxane and silicone rubber under the action of catalyst. Silicone pressure sensitive adhesive.

The indicators for measuring the adhesive properties of pressure-sensitive adhesives are tack T, adhesion A, cohesion C and keying K, to obtain excellent pressure-sensitive adhesives. It must be considered how to make the four bonding forces satisfy the following balance relationship: K > C > A > T. It is concluded that the performance of silicone resin and rubber material has the greatest influence on the performance of pressure sensitive adhesive. With the increase of the amount of silicone resin, the cohesive force of pressure sensitive adhesive increases, but the peeling force decreases. With the increase of the amount of silicone rubber, the initial viscosity increases. But the viscosity is reduced. This is because silicone rubber can increase the fluidity of the pressure-sensitive adhesive, thereby increasing the interfacial adhesion, and the initial tack is strong; the amount of the resin is reduced, which is not conducive to deep cross-linking, the reinforcing effect is poor, and the cohesive force is lowered. The molecular quality of the MQ resin has a great influence on the adhesive properties of the pressure sensitive adhesive, because the change in molecular mass changes the viscosity and cohesive strength of the pressure sensitive adhesive. When the molecular weight is high, the pressure sensitive adhesive has high cohesive strength and good viscosity; the molecular weight is low, the bulk viscosity is low, and the interfacial adhesion can be improved, but the polymer has low cohesive strength and is liable to cause cohesive failure during peeling. When the molecular weight distribution of MQ resin is wide and the number average molecular mass is about 3000, it can be used to prepare pressure sensitive adhesive. Nicolas studied the adhesion of acrylic adhesives to silicone elastomers containing different masses of MQ silicone to adjust the mechanical properties of the tape (mainly peel strength). The results show that the amount of MQ silicone resin in the elastomer has a great influence on the performance of the modified tape, and controlling the surface properties of the elastomer is an effective method for adjusting the peeling force.

4 other applications
It can be used to prepare silicone defoaming agent with high temperature resistance and alkali resistance. The defoaming agent also has the advantages of non-toxicity and environmental protection. The high-viscosity hydroxy silicone oil and MQ silicone resin are added to synthesize a highly branched network polymer, thereby improving the high temperature resistance and alkali resistance of the antifoaming agent. Using a Si-based or aralkyl-containing MQ silicone resin as a crosslinking agent, a phenyl silicone-containing encapsulating material is synthesized with a vinyl-containing, high-phenyl-containing silicone resin under the action of a platinum catalyst, and the material compatibility and It has good transparency, high hardness and high refractive index, and can be used for LED packaging and lens fabrication. The MQ-containing hydrogenated silicone oil and the silyl enoate are subjected to a hydrosilylation reaction under the catalysis of Pt to obtain an MQ resin-modified carboxy silicone oil. Its combination with an amino silicone oil emulsion gives the fabric a softer, smoother, fuller feel.